The present invention relates to a waveform equalizing circuit, and more particularly to a circuit for processing a signal waveform read out by a magnetic head in a magnetic recording device so that the recording/reproducing characteristic of the magnetic recording device is equivalently improved.
A magnetic recording device such as a magnetic disc device is required to become larger in capacity and higher in recording density with the years. In order to attain a high recording density, it is necessary to enhance a bit density and a track density. The bit density can be made high by improving the performance of each a magnetic head and a magnetic recording medium and reducing the spacing between the head and recording medium.
However, a further improvement in each of the head and recording medium has become difficult. In recent years, there have been used such techniques as a signal waveform read out by the head is processed by a reproducing circuit so that the recording/reproducing characteristic of the magnetic recording device is equivalently improved.
As one of the above-mentioned techniques, a waveform equalizing circuit shown in FIG. 1 is known which is made up of a delay line 4, an attenuator 5 and a differential amplifier 3. Referring to FIG. 2, a side lobe of an input waveform 1 (indicated by a solid curve) read out by a magnetic head is cut off by the waveform equalizing circuit, and therefore an output 2 (indicated by a dotted curve) from the waveform equalizing circuit becomes small in spread of waveform. Accordingly, a frequency-characteristic of reproduced signal indicated by a solid line 6 in FIG. 3 is improved as indicated by a dotted line 7, and thus a pattern peak shift can be reduced.
The pattern peak shift is generated mainly by the intersymbol interference in a read-out waveform, and is small as the read-out waveform is narrower in width and sharper.
In magnetic recording devices, owing to variations in the characteristics of magnetic heads and magnetic recording mediums, the characteristic of reproduced waveform (especially, the width thereof) varies widely. Specifically, in a magnetic disc device, a waveform reproduced from an inner track on a magnetic disc is different from that reproduced from an outer track in the characteristic (or width) of waveform. That is, the pattern peak shift varies considerably, and therefore it is difficult to obtain an excellent recording/reproducing characteristic. In other words, in the conventional equalization circuit, since circuit constants such as a delay time and an attenuation factor are fixed, the effect of equalization, that is, a decrease in pattern peak shift is kept constant, and therefore equalization is excessive for some waveforms and deficient for other waveforms.